Lightwave communication systems typically employ optical amplifiers as in-line amplifiers for boosting signal levels to compensate for losses in a transmission path, as power amplifiers for increasing transmitter power, and as pre-amplifiers for boosting signal levels before receivers. In a wavelength division multiplexing (WDM) system, in which many optical channels at different wavelengths are combined into a composite optical signal, optical amplifiers are particularly useful because of their ability to amplify many optical channels simultaneously. Typical amplification schemes include optical amplifiers that employ rare earth-doped fiber amplifiers, such as erbium-doped fiber amplifiers, which are pumped with diode lasers, and Raman amplification in which diode-laser pumping generates gain through stimulated Raman scattering in an optical fiber.
As is well known, the performance of optical amplifiers can be affected by the aging of components, temperature-induced variations, and other factors. As such, various monitoring techniques are often used to detect and report anomalies so that corrective action can be taken. In some systems, for example, a separate supervisory optical channel (e.g., telemetry channel) may be used for communications between network elements. Some conventional uses of the supervisory channel include network monitoring functions, alarm reporting and indications, messaging, maintenance, and so on. In the alarm application, for example, the supervisory channel can be used to carry an alarm indication or signal between network elements so that appropriate action can then be taken by the respective network elements. The supervisory optical channel is assigned a separate wavelength, typically out of band, from the other traffic-carrying optical channels (wavelengths).
In conventional arrangements, the supervisory channel is typically processed using components in the optical amplifiers. For example, optical amplifiers include components for receiving, detecting, filtering (for add/drop), converting (e.g., optical to electrical to optical), and regenerating the supervisory channel at each node. In this manner, the supervisory channel can be processed at each node to carry out the aforementioned monitoring and reporting functions. However, processing the supervisory channel at each optical amplifier node adds complexity and cost to the optical amplifiers.